Device foe dry separation of pke-



Dec. 10, 1940. L. E. BIGELOW I DEVICE FOR DRY SEPARATION OF PRECIOUS METALS FROM FINELY DIVIDED MATERIAL Original Filed Sept. 7, 1935 7 av v HARRIJ, Inst/l, Fosrcn a HARRIJ 41. a FOR 7'!!! 114M A TTOQNEKS Rciuued 10, 1940' DEVICE FOR DRY SEPARATION OF PRE- CIOUS METALS FROM FINELY DIVIDED MATERIAL Leroy E. Bigelow, Manhattan Beach, Calif.

Original No. 2,160,822, dated June 6, 1939, Serial No. 39,595, September 7, 1935. Application for reissue July is, 1939, Serial No. 285,074

-9 Claims. (Cl. 209-131) My invention relates to a device for the dry separation of precious metals such as gold, silver, platinum and the like from finely divided material. Without limiting this invention and setting the following forth merely as one example, I have found that my invention is well suited for the dry separation of finely divided previous metals, such as gold, from finely divided dry material, such as desert sand.

It is an object of my invention to provide .a I

machine which will separate and remove 'by gravity the heavier particles of precious metals, as gold from finely divided material.

It is a further object of my invention to provide mechanism which will permit the lighter particles of precious metals, such as flour gold,

to be suspended in air and electrostatically removed from such suspension;

It is anotlier object of my invention to provide a device employing an air flotation process having a plurality of chambers, each of which has separately controlled air pressure, permitting adjustment of the rate of flow of materials through the separating device.

It is another object of my invention to provide -electrostatically charged plates of a particular shape, which will aid in the separation of the relatively light precious metals from the finely divided material.

The above mentioned general objects of my Fig. 3 is a detached fragmentary sectional view on a larger scale of parts of the air blast means;

Fig. 4 is a detached fragmentary plan view of parts of the air blast means;

Fig. 5 is a fragmentary sectional view of a modified form of trough means-positioned below the electrostatically charged plates; and

' Fig. 6 is a detached fragmentary sectional view of a modified form of electrostatically charged plate.

- In the drawing a substantially closed receptacle I0 is connected at one end with a hopper H and a gate valve I! may be opened and closed to permit the material in the hopper II to pass downbers 25 to 23, inclusive.

wardly in the chute l3 into the receptacle ID. A gravity closing inlet valve is preferably provided which remains open as long as material is passing downwardly from the hopper ll into the receptacle ID. The gravity closing inlet valve l4 comprises a valve member I5 supported by pivot l6 and provided with a longitudinally adjustable counterweight means 11. The counterweight means I1 is longitudinally adjusted on the lever l8, so that any appreciable weight of materials present on-the gate I5 w maintain the gravity closing valve means M in qpen position. In the absence of material on the gate l5, the weight I! moves the valve means it into closed position.

At the other end and on the bottom of the receptacle Ill is an outlet valve means [9. This outlet valve means i9 is also preferably a, gravity" closing valve and is provided with a gate '20 connected with an arm or shaft 2! and a counter weight 22 which is longitudinally adjustable on the shaft 2|. justed longitudinally of the shaft 2| so thatthe outlet valve 13 will be maintained; open with the presence of a predetermined amount of material on the gate 20. A substantially horizontal screen section 23 is provided adjacent the outlet end portion of the machine and a substantially inclined The counterweight 22 may be ad-- screen section 24 is provided substantially adjacent the inletend portion of the machine.

A plurality of chambers, such as chambers 25, 26, and 21, are provided below the screen section 23. chambers 28 and 29, are provided below the inclined screen section 24. An air reservoir 30 is connected to asource of air pressure, as a blower 3|, which is driven by any suitable source of power, 'such as an electric motor 32 and belt means 33. The reservoir 30 is connected by separate conduits 34, each of which is provided with a separately adjustable valve means 35, with the chambers 25 to 29 inclusive. For purposes hereinafter discussed, by the adjustment of a valve 35, any desired pressure may be created in the chambers 25 to- 29, inclusive. The screen sections 23 and 24, which form the upper surface of the chambers 25 to 29, inclusive, are of a sufficiently fine mesh to prevent the passage of material downwardly therethrough into the cham- In providing such screen for relatively fine material, I havetaken a 500 mesh screen of approximately 3*, inch thickness and rolled said screen to provide smaller openings in the screen. After the screen was rolled, it is believed that the openings in such a screen were of a size approximately equal to the open Another plurality of chambers, such as ings in a 750 mesh screen. For coarser material, a coarser screen may be used. The Purpose of providing relatively flne openings in the screen sections 23 and 24 is to prevent material passing downwardly therethrough and at the sametime to provide openings which will permit the desired air pressure in the chambers 25 to 29 to be maintained. I have found in operation that pressures ranging up to twenty pounds are necessary for diflerent types of material in the respective chambers 29 to 29, inclusive.

The relatively light precious metals, suchas flour gold,'is recovered in what may 'lxe termed an "air flotation zone in the upper portion of the receptacle In above the screen section 23. The eflect of the air breaking through the blanket of material from below is to form a cloud of air-borne flnely divided material, and a feature of my invention is that I provide electrostatically charged plates, as indicated by numerals 39 and 31, in the air flotation zone for extracting values from this cloud. To favor air currents in the air flotation zone for carrying the finely divided material intothe region of the electrostatically charged plates 38 and 31, Iwprovide one or more air flotation outlets 31' in the end of the receptacle l0 well above the outlet valve means H. In the particular embodiment being described two such openings 31' are shown on two levels corresponding to ,two horizontal.

series of the electrosatically charged plates 36 and 31.

'The end wall as or the receptacle III is pref-- erably inclined at an angle of substantially 45. The lower end of the inclined wall 38 is in spaced relation to the lower end of the inclined screen section 24 providing between said members a discharge outlet chamber or' trap 44 for heavy particles of material. Preferably a plurality of air conduits, such as conduits 39 and 39, are provided in the discharge outlet chamber 44. The air conduit 39 is preferably positioned near the lower end of the chamber 44- and the air conduit 39' is preferably positioned adjacent the upper opening of the chamber 44.

, Conduit means 43 connects the air conduits 39 and 39? with the air reservoir 39. A valve is provided in the wnduit 40 for adjusting the air pressure to the conduits 39 and 39'. The

nection between the conduits 39' and 49 main- An angularly disposed plate ii is preferably provided above the air conduit 39'.

A chamber 31 is provided addacent the end wall 33 in communication with the interior of the machine. A screen 33 forms a continuation oi the wall 33 and extends over the opening between the chamber 31 and the interior of the machine. An air pressure supply conduit 39 having a valve ll therein is connectedwith the chamber 31. The conduit 33 is connected with the air reservoir 33, preferably by connecting said conduit 83 with the conduit 49 between the valvell'andsaidairreservoir.

These rolls are preferably driven at relatively slow speeds from a source of power, as the electric motor 32, by means of a belt 46; a clutch mechanism 41, a speed reduction means 49 and a belt 49. The drive means and clutch mechanism, for independently controlling the operation of therolls '45, is only somewhat diagrammatically indicated. However, as this may be done by'manywell known means, it is believed that such diagrammatic indication is sufficient. The

air from the conduit 39 and 39' tends to keep the.

finely divided material in the chamber 44 in a 7 state of agitation permitting the heavier particles to move downwardly to the bottom" of the chamher. The heavier particles pass downwardly between the rubber rolls into the receptacle 50.

The liner particles of metal and the flnely divided materials pass upwardly to "maintain the level which is indicated at 5|. As thematerial rises, due to the action of the air from the conduits 39 and 39' and chamber 61, it passes in the direction of the arrow between the wall 38 and the baiile plate 43. screen section 24 and the wall 33 are inclined toward each other to form a substantially. V- shaped hopper, a relatively large body of material must be maintained in, agitation over said members, as compared to the amount of material which remains in agitation over the screen member 23. The air passing through the conduits. 39 and 39', together with the air passing through the screen sections 24 and 63, is sumcient to maintain the material in agitation above .said screen section 24 and said wall 39.

The particles of metals which are of a size smaller than the size of particles which have been separated out, and which ran down the wall 33 into the chamber 44, movewlth the material .in the substantially V-shaped hopper in a substantially rotary direction.- These particles are deposited onthe screen section 24 and graduate.

in size, the heavier'being deposited on the screen section directly above the chamber 29, while the lighter are deposited on the screen section 24 above the chamber 23. Also due to the agitation In view of the fact that the of the material directly abovetgle screen sectively heavy particles and a sloping portion for accumulating particles of intermediate size.

Electrostatically charged plates arealso used to complete the separation of the metallic substances from the flnely divided materiaL, The electrostatically charged plates 33 and 31. which are positioned above the screen section .23, and

which are shown in plan in Fig. 2, together with theelectrostatically charged plates 54 and 99,

which are present in the chamber 26, are spaced apart from approximately 34;" to 2" depending upon the class of material in the machine. The plates 36 and 54 are the positive plates, while the plates 31 and 66 are the negative plates. It is desirable that as high a voltage of direct current be impressed on these plates as may be done without the electrical energy arcing from one plate to the other. In view of the fact that such information is well known in the electrical art, I will not set forth complete data relative to spacing and strength of voltage. use a voltage of at least 2,000 volts-the exact voltage depending upon the spacing between the plates. For convenience, may be rectified by well known means, and the resulting pulsating current 01 the desired voltage, having a relatively low amperage, is very satisfactory and suitable for impressing a voltage on the said plates. As relatively high voltage electrical energy is discharged between the plates 66 and 64 (without arcing, as above indicated), the positive plates 64 tend to electrostatically attract non-magnetic, as well as magnetic metals toward said positive plates. This force attracting the non-magnetic precious metals toward the plates 64 tends to maintain the same against the inclined screen section 24. In view of the teat that the openings in the screen .are small, relatively fine particles oi precious metals cannot pass ther'ethrough. The presence 01' the electrostatically charged plates 64 at this position serves as means to prevent the precious metals of a size larger than flour gold from moving with the finely divided materials toward the discharge end 01' the machine.

-Thus far, the heavier and relatively lighter particles of metals have been separated out .of the mass of finely divided material. In some desert sand, a great amount of values in-the form of flour gold are found. A certain amount of these values willbe in the finely divided material as it passes over the screen section 23. As such values pass over this screen section 23 the air passing upwardly through said'screen will carry the said values upwardly into the field or the plates 36 and 61. Also the air which raised the particles of such finely divided precious metal adjacent the bailie 43, raised this finely divided metal or flour gold into -the field oi the plates 36 and 31. The plates 36, being positively charged,

will electrostatically attract the flour gold to said shown an alternative form oi plate which may 1 .be substituted tor the plate 36. Thisplate shown in Fig. 6 is provided with integral inclined'sections 68 and 69 formed by punching out sections oi the metal of the plate in alternate directions,

leaving openings 60. Material, passing from anupper portion towards lower portion of the plate shown in Fig. 6, will be directed by the inclined sections 66 and 59 and may pass alternately from one side of said plate to the other and ultimately from the lower edge of said plate into the troughlike member '66. This particularly shaped plate seemsto aid in-retaining the flour gold on', the plates.

However, I prefer to alternating current closingintake valve H.

I 63 is provided so that the values recovered in the chamber '50 may be conveniently removed. To obtain the values which are recovered by the plates 36, it is preferable that the plates be of such construction that they may be readily removed from the machine. This may be done by mounting the plates 36 and 31 in trays 65, which trays are slidable into and out of the machine. The plates 36 and 31 preferably slide vertically into slots 66, which are provided at spaced intervals in the sides of the trays, whereby plates may be readily removed from the trays individually. It will benoted that the flotation outlets .31 are provided in the trays 65. and that the rate 01' discharge of flotation air may be increased by pulling out either or both of the trays to a slight extent as indicated in dotted lines at 30' in Fig. 1.

After the plates are removed from the machine, the values, which are in the troughs 66, may be readily recovered and the values which have collected on the plates 36 may be removed by scraping the plates. In the event that mercury has been used, the amalgam containing such values may be scraped from the plates. The

concentrates thus recovered from the plates 36, the troughs 56 and from the chamber 50 may be further refined by well known apparatus.

' In the operation oi! the apparatus described, the finely divided material, which may be as above indicated desert sand or artificially produced finely divided material, is placed in the hopper II and permitted to discharge from said hopper past the gate valve l2 and past the gravity Whensuch finely divided material enters the relatively closed receptacle l0, it is agitated by the air until the same substantially assumes the level indicated at 6|. As the supply of material is increased, the gravity closing discharge means willopen, due to the presence of material thereon, and as the agitated mass 01' finely divided material attempts to seek its own level, it discharges from the gravity actuated discharge valve means I9, and out the chute 64. To increase the rate of discharge of the material it is only necessary to adjust an individual valve means 360! a chamber 25, 26 or 21. As the pressure in said chambers is in reased,-the rate means for readily adjusting the rate oi now of the material through the receptacle, which rate should be determined to be the maximum rate material, having a high percentage of relatively s fine or flour gold, is being rim through the machine, then the rate of flow should be less to per,-'

mit all of such flour gold to be recovered by the electrostaticallycharged plates and to thereby provide .a maximum recovery of such values..

Also in the event that the material is in an extremely fine state of subdivision, the pressures in the chambers 25, 28 and I1 below the screen section 23 must be decreased and the pressures in the chambers 28 and 29 and in the conduit 39 must be relatively decreased to provide suflicient agitation of the finely divided material to effect a most efllcient operation of the device.

The granular material tends to form a blanket continuously flowing toward the outlet valve means I! because any large body of finely divided material is fluid to a degree and because the fluid character of such material in my apparatus is accentuated by continuous agitation. The compressed-airunder the material-supporting screen continually breaks through the blanket of material at numerous points so that the material has the appearance of boiling. Because of the "boiling" action the, material of the blanket-like stream is, for the most part, at any given moment spaced slightly above the screen. In practice the apparatus is operated continuously for substantial periods, and during such periods of operation the blanket of-material is continuously discharged through the outlet valve means I! and the air- 1. A device for the dry concentration of precious metals from finely divided material, com-- prising a receptacle; material inlet means at one end portion of the receptacle and material outlet means at the other end portion of the receptacle; a screen like bottom of fine mesh in said receptacle supporting finely divided material and allowingthe passage of air therethrough, said screen like bottom having a section upwardly inclining from the inlet end portion toward the outlet end portion, and a substantially horizontal section extending from the inclined section toward the outlet end portion; air pressure supply means operatively positioned below said screen and directing a blast of air upwardly through said screen and said material; metal plates positioned below and adjacent to said inclined screen section; and

means impressing a relatively high voltage on said plates.

2. A device for the dry concentration of precious metals from' finely divided material, comprising a receptacle; material inlet means at one end portionof the receptacle and material outlet means at the othei'end portion of the receptacle;

a screen like bottom of fine mesh in said recepta.--

cle supporting finely divided material and allowing the e of air therethrough, said screen like bottom having a section upwardly inclining from the inlet end portion toward the outlet end portion, and a substantially horizontal section extending from the inclined section toward the outlet end portion; air pressure supply means operatively positioned below said screen and diand said material; discharge outlet meansfor heavy particles of material positioned adjacent the lower end portion of the inclined screen section; air seal means operatively positioned as respects said discharge outlet means; and means means at the other end portion of the receptacle; a screen like bottom of fine mesh in said receptacle supporting finely divided material and allowing the passage of air therethrough, said screen like bottom having a section upwardly inclining from the inlet end portion toward the outlet end portion, and a substantially horizontal section extending from the inclined section toward the outlet end portion; air pressure supply means operatively positioned below said screen and directing a blast of air upwardly-through said screen andsaid material; discharge outlet means for heavy particles of material positioned adjacent the lower end portion of said inclined screen section; two driven rolls of soft rubber operatively positioned in said discharge outlet means discharging said heavy particles therefrom and maintaining a substantial air seal, and means positioned within said receptacle and discharging ablast of air into said discharge outlet means, whereby material will be urged against entering said outlet means.

4. A device for the dry concentration of precious metals from finely divided material, comprising a'receptacle, material outlet means at,

one end portion of the receptacle; material inlet means at the other end portion of said receptacle;

' an inclined wall below said material inlet'means;

a screen like bottom-of fine mesh in said recep-' tacle supporting finely divided .material and.

allowing the e of air therethrough, said screen like bottom having an inclined section with its lower end positioned adjacent the lower end of said inclined wall; discharge outlet means for heavy particles of material positioned adjacent the lower end of said inclined screen sectionand said inclined wall; means positioned within said receptacle anddischarging a blast of air at the location of said discharge outlet means; and means discharging air upwardly 'material inlet to said material outlet, at least a portion'of said bottom wall being perforate, there being an air flotation zone above said bottom wall, said bottom wall being of broken configuration in longitudinal section to form at least one trap for local accumulation of the coarser metal particles; means for maintaining air underpressure under the perforate portion of said bottom wall to cause air to stream upward therethrough to agitate the material thereon, to cause the material to travel over said bottom wall in a moving blanket toward said outlet means and to form above said blanket in said air flotation zone. a cloud of the finer intermixed particles from the blanket moving to said air flotation outlet means:

electrostatic means in said air flotation zone to extract the metal particles from said cloud; and means to direct air upward through said trap,

thereby agitating the material therein to permit the larger particles of metal to gravitate to the bottom of the trap.

.6. A combination as set forth in claim in which the bottom of said trap is sealed in part which the bottom of said trap is sealed by a pair of coacting rolls of resilient material adapted to deliver accumulated metal particles from the trap.

8. A device of the character described for extracting valuable metal particles of varying size from a granular mixture of materials, comprising: a substantially closed-in receptacle having material inlet means, material outlet means, and flotation outlet means; means providing a wall in said receptacle for supporting material in progress from said material inlet means to said material outlet means, at least a portion of said wall being perforate, there being an air flotation zone in said receptacle above said wall; means for maintaining air. under pressure under said perforate portion of said wall to cause air to stream upward through said perforate portion to agitate the material thereon, to cause the material to travel over said perforate portion in a moving blanket toward said material outlet means, and to form in said air flotation zone above said blanket a cloud of the finer intermixed particles from the blanket moving-to said air flotation outlet means; electrostatic means in said air flotation zone to extract valuable particles from said cloud; and electrostatically charged means spaced below said material supporting wall to favor immobilization of metal particles thereon.

9. A device of the character described for extracting valuable metal particles of varying size from a granular mixture of materials, comprising: a. substantially closed-in receptacle having material inlet means, material outlet means, and air flotation outlet means; means providing a wall in said receptacle for supporting material in progress from said material inlet means to said material outlet means, at least a portion of said wall sloping upward toward said material outlet means to favor accumulation of metal particlesthereon, there being an air flotation zone in said receptacle above said wall; means for maintaining air under pressure under said perforate portion of said wall to cause. air to stream upward through said perforate portion to agitate the material thereon, to cause the material to travel over said perforate portion in a moving blanket toward said material outlet means, and to form in said air flotation zone above .said blanket a cloud of the finer intermixed particles from the blanket moving to said air flotation outlet means; electrostatic means in said air flotation zone to extract valuable particles from said cloud; and electrostatically charged means spaced below said inclined portion 01' the material supporting wall to immobilize said metal particles accumulated thereon.

LEROY E. BIGELOW. 

